Griffin Powermate evdev setup

David Hagood david.hagood at
Wed Apr 29 04:56:47 PDT 2009

I'd like to ask a more general question about devices which, like the
Powermate, don't really fit into either the "Keyboard" or "Pointing
device" classes:

To what extent *should* X support these devices?

Let's examine a ShuttlePro - a jog wheel, a spinner, 15 buttons. It's
not really a keyboard, as the buttons don't really have any defined
mapping other than "Button 1" ... "Button 15". It's not a pointing

Applications like Kino recognize it and can use it to do editing
control, in which case the jog wheel and the spinner are logically
distinct from the mouse's wheel. Kino supports this device by going
directly to the underlying /dev/input/event device, and not through X.

Now, that works - and perhaps that is how it should be: X concerns
itself with pointers and keyboards, and we let other things be handled
outside of X.

HOWEVER, that approach has several problems:
1) No remote access: I cannot run a program on another machine and have
it use the Shuttle unless the Shuttle is supported by X.
2) No arbitration between applications: If Kino and some other program
Foo both "understand" the Shuttle and want to use it, and I change input
focus from Kino to Foo, how do we route the events correctly? Do the
programs close the device when the lose input focus, and re-open it when
the regain focus? Do they ignore events when not focused?
3) Less portable code - going to /dev/input/event5 may be fine under
Linux, but is it supported under the *BSD kernels? under the Mac's X
server? under Solaris/Irix/AIX?

You can generalize this to things like joysticks and game pads - as far
as I can see, there is little difference between a Shuttle and my PS3
DualShock as far as things like this go.

Has there been a design decision where support for devices like this
should live?

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